There are circumstances where it is advantageous to employ paper having enhanced friction at the surface. Paperboard liner for cardboard (corrugated) boxes is an example, as in the case of shipping or otherwise transporting stacked boxes containing expensive goods, or goods easily susceptible to damage in the event the stack topples. This problem can be surmounted to a considerable extent if the surfaces of the boxes are treated to increase their friction, meaning more resistance to sliding.
The same case prevails in the manufacture of box blanks. The two liner boards are adhesively joined to opposite sides of the fluted center in a continuous production stream. The three components (two outside liner boards and one fluted inside center) are supplied from separate winders at the board plant and are continuously combined at a juncture or confluence after being coated with an adhesive to secure the lamination; afterwards the continuous, laminated, corrugated board is die cut and scored to comply with the box geometry. The clones are separated and stacked flat; again it is advantageous that the exposed liner surfaces be treated to increase the friction, to keep the stack in a neat order.
It will be appreciated a similar case applies for the benefit of frictionizing paper (Kraft) bags.
The proposition of treating the liner board by spraying it with a friction enhancer is not new: U.S. Pat. Nos. 3,649,348, 3,689,431 and 3,860,431. Further, in U.S. Pat. No. 4,418,111 it is proposed to rely on a mixture of silica sol and urea. The urea is said to preserve the frictioned surface against loss of friction coefficient, that is, the slide angle is less susceptible to decline as a result of rewinding the paper.
It may also be mentioned in connection with the foregoing that either at the paper mill or board manufacturing plant the friction properties of the paper are tested for the so-called slide angle as will later be described in detail.